Influence of MICP on unsaturated soil properties and its application as bio-engineered slope covers on stability of slopes under varying rainfall conditions

Rapid expansion and increase in infrastructural demand for the connectivity has led to increase in construction of roads in mountainous region across the world. However, the presence/ formation of steep soil slopes and cuts along roadways pose a significant geotechnical challenge, particularly failures caused by rainfall during the monsoon. One of the methods to reduce the risk of slope failures triggered by rainfall is by adopting suitable slope covers. In this study, the suitability of microbially induced calcium precipitation (MICP) to form slope cover to enhance the stability of slope cuts/ soil slopes under varying rainfall conditions are explored through experimental and numerical studies. The influence of MICP on unsaturated soil properties, namely the soil-water characteristics curve, unsaturated hydraulic conductivity, and unsaturated shear strength parameters, which influence the characteristics of slope cover, was investigated. From laboratory studies it is observed that, the properties of MICP - treated (bio-engineered soil) are altered by the formation of calcium carbonate due to microbial activity. The air-entry value of bio-engineered soil increases from 2 kPa to 72 kPa for untreated soil, and the hydraulic conductivity of bio-engineered soil is found to decrease by 75%. Considerable increase in unsaturated shear strength parameters of bio-engineered soil is also observed. The effective cohesion ( c’ ) is found to increase from 2.86 kPa to 27.8 kPa, internal friction angle with respect to normal stress is found to increase from 12.2 ͦ to 13.9 ͦ and a negligible change in internal friction angle with respect to matric suction is observed. Numerical studies show that the presence of bio-engineered slope covers helps maintain suction in soil slopes through capillary effects. Further, it is observed that in the case of soil slopes with bio-engineered slope cover subjected to rainfall, improvement in stability and considerable reduction in deviatoric strain within the soil slopes are noted.